With the development of semiconductor technology, the degree of integration of very large semiconductor integration (VLSI) chips has reached a scale of having nearly one or even several billions of devices in a single chip. A technique with two or more layers of metal interconnections has been widely adopted to meet the development requirements.
Traditional metal interconnections are made of aluminum. However, as the feature size of devices in integrated circuits (ICs) continuously decreases, the circuit density in metal interconnections steadily increases and the required responding time is continuously reduced. Therefore, the traditional aluminum interconnections cannot meet the requirement and, thus, a copper interconnection technique has gradually used to replace the aluminum interconnection technique.
Compared to aluminum, copper shows lower electrical resistivity and higher electromigration resistance. Therefore, using copper interconnections, resistor-capacitor (RC) delay of interconnections may be reduced, electromigration resistance may be improved and, thus, stability of the device may also be improved.
However, the existing copper interconnection technique may still have its drawbacks. Specifically, as a metal, copper still has relatively high migration mobility, thus diffusion of copper atoms in silicon and silicon oxides as well as in most of dielectric materials is very quick. Further, once copper atoms are diffused into semiconductor substrate or dielectric layer, the life time of the minority charge carriers in the device and the leakage current in the junction may be affected. In addition, as copper atoms diffused into semiconductor substrate or dielectric layer, electromigration in the semiconductor structure may also increase, which may further cause circuit failure in the semiconductor structure and degradation of the reliability. Being distinct from aluminum interconnections, where failure of the aluminum interconnections is caused by diffusion of aluminum atoms along the boundary of grains, the electromigration failure in copper interconnections may be caused by diffusion of copper atoms along surfaces and interfaces.
When using the copper interconnection technique to fabricate semiconductor structures, the electromigration problems may still be prominent and the electrical performance of the semiconductor structures may also need to be improved. The fabrication method and device structure in the present disclosure are directed to solve one or more problems set forth above and other problems in the art.